Wire and thermoplastic high pressure hoses are ubiquitous. So much so that the Society of Automotive Engineers (SAE) has adopted detailed standards that describe the materials used in their construction, dimensional tolerances and the dynamic test parameters for a wide range of rubber and thermoplastic high pressure hoses. One such standard is SAE J517:2008 with the subheadings of SAE100R1, SAE100R2, SAE100R16 and SAE100R17.
The processes for manufacturing high performance wire reinforced rubber hoses were generally devised in the first half of the last century. This was an era where energy, space and labor were cheap and environmental awareness was simply not a major consideration of process design. Certainly, advances have been made, but the basic process remains more or less the same.
The traditional method of manufacturing high performance, high pressure, steel wire braided rubber hose is well known: As a first step, a semi-flexible polymeric solid continuous mandrel is extruded. As a second step, a rubber tube is extruded over said mandrel. As a third step, wire reinforcement in the form of a plurality of high tensile strength steel wire is applied over the outer surface in the form of a braided or spirally wound structure. As a fourth step, a rubber cover is extruded over the outside of the wire structure. As a fifth step, the wire structure is encapsulated in a textile tape or a semi-rigid thermoplastic sheath. As a sixth step, the sheathed structure is cured using some form of heating apparatus. Generally speaking this process is carried out by placing the uncured hose structure into a steam autoclave for a specified period of time so as to accomplish curing or vulcanization of the structure. As a seventh step, the formerly applied textile tape or semi-rigid thermoplastic sheath is removed. As an eight step, the mandrel is removed from the inner tube and for all intents and purposes, the hose is finished.
There have been attempts over the years to reduce the number of steps described above that have resulted in some reduction or combining of the eight basic steps noted. Most of those methods have been driven with cost savings as their main thrust. However, generally speaking, the mandrel manufacture and use, the curing process, the mandrel removal are all necessary components to manufacturing a wire reinforced rubber high pressure hose suitable for the purposes desired and are widely in use today.
The use of thermoplastic in hose design has been one means of reducing the complicated steps associated with a cured rubber hose. Such a process can be reduced in its most basic form to three steps. The first step is to extrude a thermoplastic tube. As a second step, the tube is reinforced with braiding of yarn or steel. The third step is to apply a cover material.
Hoses that are reinforced with yarn are also well known in the field. Within the SAE J517 standard, there is an applicable subheading for such products known as SAE100R7. Because such hoses do not incorporate wire as the pressure support, they are prone to kinking, can be cut through if impacted by something sharp and are generally known to be quite stiff.
To date, there is no subheading within J517 for a wire braided thermoplastic high pressure hose. While the basic steps for manufacturing a wire braided thermoplastic hose have been reduced from eight to three, the prior art processes add too much complexity and risk to the three steps. This is because historically, such hoses have been made using complicated and expensive manufacturing techniques and are comprised of expensive engineered thermoplastic materials. In spite of such complexity and risk, the prior art processes do not produce improved hoses, especially in the area of pinhole prevention and lamination of the various layers. Additionally, the resulting hoses of such methods are relatively stiff due to the use of mostly semi-rigid thermoplastic materials.
Two such examples of prior art are Chermak U.S. Pat. No. 4,341,578 and Washkewicz U.S. Pat. No. 4,952,262. Both patents describe a method of extruding a thermoplastic tube, applying braided steel wire reinforcement and extruding a cover over the reinforcement. Both patents advocate a method of heating the outside of the wire braid through an extra induction heating method and both advocate the pressurization of the inner tube with compressed air as a means of intentionally protruding the outer surface of the inner tube into contact with the small interstices between the wire braid layers.
FIG. 1 illustrates the structure of the hose of the Chermak U.S. Pat. No. 4,341,578 and demonstrates the result graphically, depicting protrusion 10 of the inner tube 12 through the interstices of the braid layer 14 and on through to the outside of the braid layer and into the outer tube 16. Chermak runs an unacceptably high risk of pin holes caused by protrusion 10 from within the inner tube 12. This is due to the high amount of heat applied throughout the structure and the pressure from within the tube being applied during the process
FIG. 2 illustrates the structure of the hose of the “Washkewicz” U.S. Pat. No. 4,952,262 and depicts the protrusion 20 from both sides 22 and 26 of the braid layer 24. This results from the inner tube 22 being forced under pressure while the outer cover 26 is extruded through the conductively heated wire braid structure 24 to protrude through the interior of the braid layer 24. As taught by Washkiewicz, such protrusion 20 of the outside of the inner tube 22 is risky and prone to producing so called pin hole leaks as the pressure from the inside of the tube combined with the heated wire 24 and the pressure and temperature of the extruder head and the melted extrudate are very difficult to control.
Washkiewicz attempts to mitigate the limitations of Chermak, but still produces an unacceptably high risk of pinholes caused by protrusion from the outside through the heated wire and inner tube. This is due to the methods applied by Chermak and Washkiewicz which can result in an imbalance between competing thermal and pressure zones.
FIG. 3 is another example of prior art showing the hose of Pianetto U.S. Pat. No. 7,222,644. The disadvantages of this hose concept are numerous. Pianetto advocates the use of highly flexible inner tube materials and a method that does not thermally bond the layers together. Such bonding of the layers is desirable in high performance hoses such as those described in SAEJ517. In Pianetto, the outside thermoplastic layer 36 does not come into contact with the inside thermoplastic layer 32 leaving voids 30 in the braid layer 34. Pianetto teaches that optionally, a layer of adhesive can be applied to bond and fill the voids between the layers. The disadvantages of Pianetto are evident by the relative low performance of the hose of no more than 30,000 impulses at only 25% of the minimum burst rating of up to 16,000 PSI simultaneously with fluid at a maximum temperature of 140° Fahrenheit. By comparison an SAEJ517, SAE100R16, compliant product whereby a nominal ⅜″ diameter hose has to meet a minimum of 200,000 impulses 33% of the minimum burst rating of 16,000 PSI at 212° Fahrenheit. The methods for measuring burst pressure, impulse, temperature, etc. are well known to those familiar in the art and described in detail with the SAE J517 document.
Further, Pianetto discloses conventional hoses braided to an angle of 1.4 or less, yet teaches a braid angle of at least about 1.4 or more. To those familiar with the art, the definition is universally defined as “pitch”. Pitch is defined at the length in inches that it takes for the helically wound plurality of wire strips to make a full revolution around the circumference of the hose tube. It is well known to those familiar with the art that such a long pitch would result in a hose that will likely change in length when impulse tested. Excessive change in length is a major factor contributing to low impulse performance.
Lastly, Pianetto teaches the use of an adhesive using a known hazardous material, Methyl Ethyl Ketone (MEK) as part of a process to impart adhesion. MEK is considered extremely flammable and prolonged exposure to MEK is well documented as being a hazard to humans and the environment.
Moreover, high pressure wire reinforced hoses have been used for decades in the field of high pressure water cleaning. As an environmental tool, water cleaning under high pressure actually uses less water than cleaning with water at low pressure. Further, high pressure agitation can accomplish many cleaning tasks without the use of chemicals. Thus, it stands to reason that environmentally sound practices should be considered when supporting the cleaning process.
As stated, the known prior art for manufacturing wire reinforced thermoplastic hose are known to be very complex, dangerous, and energy inefficient as often they use materials and processes that are poisonous to humans and the environment.
Therefore, there exists a need for an inexpensive, high performance wire braided thermoplastic hose that meets and goes beyond the minimum characteristics of traditional rubber hose. The present invention is an economical, energy and materially efficient, safe and environmentally sound method of manufacturing a high performance hose suitable for hydraulic actuation, high pressure spraying and transfer of various liquid media under high pressure.